This invention relates to a solar cell device which comprises thin film semiconductor solar cells formed on a substrate and connected in series with one another.
Solar cells arranged on a substrate have attracted attention as photoelectric conversion devices for converting sunlight or the light of a lamp into electrical energy. Each of the cells includes a semiconductor thin film, for example silicon, having a pn junction or a Schottky barrier acting as a photoelectric conversion region, and an electrode formed on both surfaces of the semiconductor thin film. However, since the solar cell has a low electromotive force, a plurality of solar cells must be connected in series and in parallel with one another in order to be useful as a power supply. When either one or more of a group of solar cells connected in series are shaded , the desired electromotive force is not generated, and the cells may be reversely biased by the electromotive force of other cells, thereby often destroying such cells. In order to prevent this disadvantage, a diode 2 has been reversely connected in parallel with one solar cell 1 to prevent the reverse bias as shown in FIG. 1, or connected in parallel with several solar cells 1 connected in series to prevent them from destruction due to the reverse bias which may occur even if only one of solar cells 1 is shaded, as shown in FIG. 2. FIGS. 1a and 2a are other examples showing series connections of cell arrangements as shown in FIGS. 1 and 2, respectively. If surge noise caused by a large external disturbance such as a thunderbolt is applied between both terminals of the solar cells connected in series, the probability that the reverse bias is added to the solar cells is made low and the reliability is increased by the diode 2. However, it is necessary for the diode 2 to be separately prepared and connected to the solar cells when the solar cell device is manufactured. Also in the conventional configuration, if an imbalance is generated among the solar cells connected in parallel, a circulating current may flow therethrough to lower the output. If some of the solar cells begin to be particularly deteriorated, the deterioration is promoted by this current, thereby increasing the output reduction. Therefore, a diode having a polarity opposite with respect to the polarity of the juction of the solar cells is connected in series with respective parallel circuits to prevent the circulating reverse current from flowing therethrough. However, again, the diodes must be separately prepared for this purpose and then connected to the circuits, thereby increasing the cost and complicating the manufacturing process. In addition, the solar cell device is inconvenient to handle because the thickness or the area thereof is increased.